Aşağıdaki gibi yol izleyebilirsin.

						
<?php
						$POST_EDILECEK_URL = 'https://www.xxx.com';
						
						$XML_VERISI = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>
										<Message xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
											<APIVersion>1.0.0</APIVersion>
											<OkUrl>https://site.com/basarili</OkUrl>
											<FailUrl>https://site.com/basarisiz</FailUrl>
											<HashData>112223445566</HashData>
											<MerchantId>12345</MerchantId>
										</Message>";
					   
						$ch = curl_init($POST_EDILECEK_URL);
						curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
						curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
						curl_setopt($ch, CURLOPT_POST, 1);
						curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/xml"));
						curl_setopt($ch, CURLOPT_POSTFIELDS, $XML_VERISI);
						curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
						$results = curl_exec($ch);
						curl_close($ch);

						//gelen cevabı okuma
						preg_match("/<donenveritag1>(.*)<\/donenveritag1>/", $results, $donenveritag1temizveri);
						preg_match("/<donenveritag2>(.*)<\/donenveritag2>/", $results, $donenveritag2temizveri);
						
						echo $donenveritag1temizveri.' '.$donenveritag2temizveri;
						?>